Advanced microwave signalling transmission networks, particularly space-deployed communication, command and control (C.sup.3) systems, require deployable antennas configured of high performance flexible reflective surfaces. For this purpose knit mesh materials have been demonstrated to provide a sufficiently high level of performance that their continued use as reflector materials can be expected in the future. Unfortunately, conventionally woven mesh structures suffer from a significant problem of high in-plane mechanical stiffness, that can manifest itself through a number of characteristics which can degrade antenna performance, including difficulty in holding surface contour manufacturing tolerances, difficulty in maintaining tension in the surface resulting from thermoelastic effects and distortion of structural support members upon which the antenna mesh is mounted (also resulting from thermoelastic effects on the mesh). As system operating frequencies continue to increase, the stiffness problem becomes more pronounced, since stiffness is inversely proportional to antenna mesh hole size which, in turn, must be made smaller to maintain RF gain.
Fortunately, there has now been developed a mesh configuration which successfully addresses the stiffness problem and is expected to continue to enjoy a degree of performance heretofore unmatched by conventional mesh structures. More particularly, in the U.S. Pat. No. 4,609,923 to Boan et al, entitled Gold-plated Tungsten Knit RF Reflective Surface, issued Sept. 2, 1986 and assigned to the assignee of the present application, there is described a new and improved antenna mesh configuration formed of small diameter (e.g. 0.4-1.5 mil diameter) gold-plated tungsten wire that has been knitted in a tricot knit configuration, so as to be able to effectively absorb thermoelastic changes in the wire and thereby retain the intended shape of the antenna. Namely, because of the inherent properties of its multiple loop structure, a tricot knit configuration is able to permit relative displacement between loops of wire at different portions of the mesh in response to environmental (thermal) changes, so that the intended contour of the antenna is effectively continuously maintained.
The present trend is toward increased RF aperture sizes for space-deployable antennas. These larger diameter structures must maintain high precision contour accuracy over the range of orbital thermal conditions to operate at the higher RF frequencies. To minimize thermoelastic distortions, materials with a near-zero coefficient of thermal expansion (CTE) become particularly attractive. Another factor closely associated with the larger diameter antenna structures is the weight contribution of the RF reflective surface itself. Materials should be selected which minimize the weight per unit area of the paraboloidal reflective surface. For example, a representative weight savings of 30-35 lbs. can be realized for a 150foot diameter antenna by utilizing low-density material for the reflective surface. Materials such as tungsten wire and molybdenum wire are utilized in the design and construction of tricot knit mesh reflective surfaces for space deployable antennas. The basic weight density of these metallic materials significantly exceeds that of some non-metallic materials. In addition, some metallic-materials are subject to sputter degradation in the presence of (non line-of-sight) nuclear radiation.